1. Technical Field
The present invention relates to a liquid detector that is adapted to detect the residual quantity of a liquid (ink) in a liquid consuming apparatus, such as an ink jet recording apparatus, and a liquid container having the liquid detector.
2. Related Art
As a representative one of known liquid consuming apparatuses, an ink jet recording apparatus is known that has an ink jet recording head for image recording. Other liquid ejecting apparatus include, for example, an apparatus that has a color material ejecting head, which is used in manufacturing color filters of a liquid crystal display or the like, an apparatus that has an electrode material (conductive paste) ejecting head, which is used in forming electrodes of an organic EL display or a field emission display (FED), an apparatus that has a bioorganic material ejecting head, which is used in manufacturing a bio chip, and an apparatus that has a sample ejecting head for ejecting a sample as a precision pipette.
In the ink jet recording apparatus, which is the representative liquid consuming apparatus, an ink jet recording head has a pressure generation unit for pressurizing a pressure generation chamber and nozzle openings for ejecting pressurized ink as ink droplets. The ink jet recording head is mounted on a carriage. Ink in an ink container is supplied to the recording head through a flow channel in succession, such that printing is continuously performed. The ink container is formed of a detachable cartridge that can be simply replaced with new one by a user when ink is consumed.
As a method of managing ink consumption of the ink cartridge, there is a method that manages ink consumption by totalizing the number of droplets ejected from the recording head or the amount of ink absorbed through maintenance using software, or a method that manages a time, at which ink of a predetermined amount is actually consumed, by attaching liquid level detection electrodes to the ink cartridge.
However, the method of managing ink consumption by totalizing the number of droplets to be ejected or the amount of ink using software has the following problems. Of the heads, there are those that eject ink droplets with a variation in weight. The variation in weight between the ink droplets does not have an effect on image quality, but the ink cartridge needs to be filled with ink in an amount with a margin, taking into consideration of a cumulative error of ink consumption due to the variation. For this reason, in some cases, ink may remain by the amount corresponding to the margin.
Meanwhile, according to method of managing the time, at which ink is consumed, by electrodes, an actual amount of ink can be detected, and thus the residual quantity of ink can be managed with high reliability. However, since this method relies upon conductivity of ink in detecting the liquid level of ink, kinds of detectable ink are limited, and the seal structure of the electrodes becomes complicated. Further, the electrodes are usually made of a noble metal having good conductivity and high corrosion resistance, and accordingly manufacturing costs of the ink cartridge may be increases. Since two electrodes need to be attached, the number of manufacturing steps may be increased, and as a result, manufacturing costs may be increased.
As one of the devices that have been developed in order to solve the above-described problems, a piezoelectric device (herein, referred to as a sensor unit) is disclosed in JP-A-2001-146030. This sensor unit monitors the residual quantity of ink in the ink cartridge using the fact that a resonant frequency of a residual vibration signal changes due to residual vibration (free vibration) of a vibrating plate after compulsory vibration between the cases of presence of ink in a sensor cavity opposite to the vibrating plate having laminated thereon a piezoelectric element and of absence of ink in the sensor cavity.
JP-A-2006-281550 discloses a technology that seals a metal sensor base with a film with a sensor chip including a piezoelectric element mounted in a concave place of a unit base, thereby forming an assembly. The sensor base of the unit base is arranged to face an ink delivery channel of the ink container.
According to the liquid detection device described in JP-A-2006-281550, a sensor cavity is provided in an ink flow channel, and ink flowing in the sensor cavity has large flow channel resistance. To solve this problem, JP-A-2006-341599 discloses a technology that provides a bypass passage communicating an upstream buffer chamber and a downstream butter chamber, which are divided by a partition wall, in addition to the flow channel of the sensor cavity.
JP-A-2006-341599 describes an example where a sensor base having a hole on each of the left and right sides is arranged in a horizontal direction, and the sensor cavity turns downward at the upper parts of both the buffer chambers. The upstream buffer chamber and the downstream buffer chamber are divided by the partition wall and arranged in parallel in a horizontal direction.
The bypass passage is provided at the lower parts of the upstream buffer chamber and the downstream buffer chamber (in JP-A-2006-341599, see claim 2 and FIG. 6).
Therefore, ink remaining in the upstream buffer chamber can be discharged to the downstream buffer chamber by the bypass passage.
According to the structures in JP-A-2006-281550 and JP-A-2006-341599, ink in the upstream buffer chamber goes toward the sensor cavity above the sensor base through a hole of the sensor base, which is formed at the upper part of the upstream buffer chamber. Accordingly, it air bubbles enter the upstream buffer chamber, the air bubbles having low specific gravity go upward in a vertical direction. For this reason, in the structures of JP-A-2006-281550 and JP-A-2006-341599, even though the upstream buffer chamber is filled with ink, that is, “ink present”, it air bubbles are mixed in ink, the air bubbles are moved to the sensor cavity, “ink absent” may be erroneously detected,
To solve this problem, the inventors have examined the sensor base which is arranged vertically or obliquely, unlike the structures described in JP-A-2006-281550 and JP-A-2006-341599. If the ink detection structure described in JP-A-2006-281550 or JP-A-2006-341599 is arranged vertically as it is, the upstream buffer chamber above the partition wall is connected to the downstream buffer chamber below the partition wall by the vertical bypass passage.
Accordingly, it is difficult to make the flow of ink toward the sensor cavity forming a part of a U-shaped flow channel independent.
According to the structures described in JP-A-2006-281550 and JP-A-2006-341599, the sensor base is also supported by the partition wall or a peripheral wall. For this reason, in a region where a slight gap is formed with respect to the sensor base, ink remains due to a capillary phenomenon. Accordingly, when the “ink absent” state is detected (air enters the cavity) white the recording head is moved and printing is performed, and the recording head returns to a home position, ink from the gap may flow into the sensor cavity and the “ink present” state may be erroneously detected. In this case, idle printing may be performed, and the lifespan of the recording head may be shortened.